Methods for increasing the efficiency of volume reduction treatment of low-level radioactive waste products have recently been disclosed. Patent Document 1 (Japanese Patent Application Publication No. 2001-153998) discloses a method for reducing the volume of an ion exchange resin which is a low-lever radioactive waste product discarded from a nuclear power facility by performing carbonization and ashing using oxygen plasma. Patent Document 1 discloses the treatment in which the resin to be treated is placed on a stage inside a vacuum vessel, and the resin located on the stage is subjected to carbonization and ashing by inducing oxygen plasma in the space above the resin.
Further, Patent Document 2 (Japanese Patent Application Publication No. 2000-275393) discloses a volume reduction treatment in which inductively coupled plasma (referred to hereinbelow as “IC plasma”) is induced for generating high-density plasma and capacitively coupled plasma is induced after the IC plasma has been stopped to decompose the tar that has adhered to the interior of the vessel.
As disclosed in Patent Document 1 and Patent Document 2, when the resin is treated, IC plasma using a high-frequency power source for generating oxygen plasma is usually used (paragraph [0012] in Patent Document 1 and paragraph [0012] in Patent Document 2). This is because it is desirable to increase the treatment amount per unit time, that is, the treatment speed, in the method for volume reduction treatment of resins, and therefore the IC plasma in which plasma density is easily increased is selected as the oxygen plasma. A power source for inducing the IC plasma is referred to hereinbelow as “ICP power source”. The ICP power source is used for initially firing, that is, igniting, the oxygen plasma, and in the conventional volume reduction methods, such as disclosed in Patent Document 1 and Patent Document 2, the ICP power source is also used for maintaining the induced state of oxygen plasma.
Patent Document 1: Japanese Patent Application Publication No. 2001-153998, for example, paragraph [0012].
Patent Document 2: Japanese Patent Application Publication No. 2000-275393, for example, paragraph [0012].